The dispersion of a pigment has been a big technical subject in the field of electrophotography, liquid development, coating, ink, cosmetics, etc. It has been a general practice to treat the surface of pigment grains or inhibit secondary agglomeration under the control of the pigment manufacturing process for the purpose of improving the dispersibility of pigment in a solvent or resin. Also for coloring grains for use in a solid or liquid developer for the development of electrostatic images in electrophotography or the like, it has been known to treat the surface of these pigment grains with various materials for the purpose of improving the dispersibility of pigment. For example, JP-A-53-17737, and JP-A-58-7648 (The term "JP-A" as used herein means an "unexamined published Japanese patent application") disclose a process which comprises treating a pigment with a silane coupling agent or titanate coupling agent in a solvent, and then heating and drying the material to allow the silane coupling agent or titanate coupling agent to be chemically bonded to the surface of pigment.
However, the known pigment surface treatment process is disadvantageous in that since a pigment which has been treated in a solvent must be withdrawn from the solvent before the subsequent treatment, secondary agglomeration of pigment grains is enhanced, possibly producing sites of maldispersion. In recent years, there is a growing tendency toward color visual system. In electrophotographic toners, too, grain transparency and colorability have been demanded more and more. It has thus been desired to provide a pigment dispersion which exhibits an improved dispersibility as compared with the prior art.
On the other hand, as a method for obtaining colored grains for use in electrophotographic toners or the like other than the conventional grinding process, there has been well known a so-called wet process, i.e., process which comprises stirring a solution consisting of an oil phase and an aqueous phase to prepare colored fine grains. In the wet process, a pigment is normally incorporated in the oil phase to prepare colored fine grains. However, this wet process is disadvantageous in that since the pigment is poorly dispersed in the oil phase or the pigment exhibits a poor affinity for an organic solvent or binder resin, colored fine grains with a poor pigment dispersibility may be formed or the pigment may be desorbed from the grains.